The lipid bilayer as an ubiquitous component of the structure of biological membranes seems firmly established on the basis of electron microscopy, chemical analysis, and physical investigations of natural organelles and their membranes. Closely associated with these structure studies are the functions of biological membranes, the most important of which is energy transduction. Insofar as the transduction of light into electrical energy and/or chemical free energy is concerned, two kinds of photoactive membrane systems have been evolved in nature, namely, the thylakoid membrane of chloroplasts and the sac membrane of photoreceptors. Ideally, a great deal of photoelectrochemistry of these pigmented lipid membrane systems can be learned from electrical measurements by placing electrodes across such membranes, much as has been done for the nerve membrane of squid axon. Unfortunately, such an approach is not yet feasible at present for most photoactive membranes, particularly those of subcellular organelles such as aforementioned thylakoids or photoreceptor sacs, owing to their minute size. Artificial pigmented bilayer lipid membranes (BLM), therefore, appear to offer the most viable system in which to investigate energy conversion processes and light-initiated redox reactions. The proposed research will be centered on the following: (1) to continue the current research program on the studies of the basic physical and electrochemistry of BLM, which should provide a more rational basis for further development; and (2) to reconstitute specific biomembrane systems with the lipid bilayer and its modifications so that simple physical, chemical and physiological processes may be isolated and analyzed in terms of the physical and chemical properties of the constituent compounds.